PHSOR09 Presentation Time: 9:40 AM

Purpose

Plesio-brachytherapy offers a favorable option for treating skin cancer or keloids post-surgical excision, particularly on curved body surfaces. By closely conforming body contours, plesio-brachytherapy can provide a more uniform surface dose compared to suboptimal external beam techniques. Current HDR flap-based brachytherapy methods, although flexible in design, can be a challenge to shape to irregular surfaces where maintaining a consistent distance for the radioactive sources is paramount to treatment goals. To address these issues, this work proposes a customized flexible silicone applicator to achieve a better fit to the patient's body with minimal air gaps.

Materials and Methods

Our plesiotherapy workflow begins with thin-cut (1mm slice) CT simulation of the treatment area for patient setup and applicator fabrication. Depending on the site, immobilization methods may be used for patient comfort and position reproducibility. A 10 mm thick bolus structure is created from the simulation image set in treatment planning system software. Applicator channel paths are designed in Autodesk Inventor (Autodesk, Inc. San Francisco, CA). Two molds are then 3D printed for surface applicator casting: an external mold is printed with PLA on an Ultimaker S7 printer (Utrecht, Netherlands) to maintain the applicator shape; and internal molds are printed with regular resin using a FormLab Form 3 printer (Somerville, MA) to house the applicator channels. Once assembled, silicone (ECO-Flex 00-30, Smooth-on) was cast into the molds. After curing, single leader flexible implant tubes are inserted into the channels and fixed in place with standard plastic buttons. The patient undergoes a second CT simulation scan for treatment planning, during which the applicator location is marked on the patient for reproducibility on treatment days. Figure 1 illustrates a 3D rendering of a silicone applicator for a vulvar and perineal surface region treatment.

Results

HDR plesiotherapy using a patient-specific flexible applicator has been successfully implemented clinically. Several patient-specific applicators have been made to treat sites (e.g. vulvar, face, buttock) with surface contours that would be difficult to treat with external beam or standard flap-based HDR brachytherapy.

Conclusions

This approach demonstrates the feasibility and effectiveness of using a silicone surface applicator in delivering targeted radiation therapy for skin cancer treatment, offering a promising option for patients with lesions in challenging anatomical locations. Future work will evaluate the use of surface-guided imaging technologies to reduce the number of CT simulations. Also, optimization strategies for catheter trajectories will also be investigated.